The present invention relates to a hydraulic circuit including multiple pumps and valve sections wherein a single main relief valve is utilized for pressure control in the circuit.
It is common in earth-working equipment, such as backhoes, front end loaders and the like, to have a bucket or shovel mounted on a tractor to be raised and lowered, tilted, or otherwise moved into the correct attitude by an appropriate mechanism for the work being performed. Such movements of the bucket, shovel or backhoe are commonly made by hydraulic cylinders supplied with fluid pressure from a suitable pump and valve arrangement.
Since a common mode of operation in earth-working is to move a bucket or the like into a pile of material, the hydraulic system for such earth-working applications may periodically require a high volume of fluid at low pressure to rapidly move the cylinder piston rods and, therefore, the bucket or the like to the work. Thereafter, low fluid volume under higher pressure may be required to provide the necessary movement of the bucket to break a portion of the material loose from a work pile or to lift the material after it is in the bucket.
A prior art approach for meeting the variable fluid demands in earth-working operations has been to provide two fixed displacement pumps to supply the required fluid under pressure for the hydraulic circuit. For example, in an application such as a loader-backhoe, a first pump flow is provided to the loader valve circuit, and the pump flow not used for the loader is combined with a second pump flow to supply the backhoe valve circuit. While the use of multiple fixed displacement pumps and valve circuits permits a more efficient system, a corresponding number of relief valves are required to provide pressure control for the multiple pump and valve arrangement.
Thus, the present invention is directed to a hydraulic circuit which eliminates the need for multiple relief valves in a system including multiple fixed displacement pumps and valve sections.